[Cbe-oss-dev] [PATCH 3/3] libspe2: Clean up proxy DMA and add error checks

[Kazunori Asayama]

Daniel Brokenshire <brokensh at us.ibm.com> wrote:
> All,
> 
> Can someone explain why it is necessary to partition the tag IDs between 
> the kernel and user?  I can not conceive of any reason why this is needed. 
>   In addition, error checking the value can result in perfectly 
> functioning applications no longer working.   Long ago, the Linux BE ABI 
> Specification stated:
> 
> "The two largest tag ID?s (30 and 31) are reserved for runtime library or 
> privileged services. The runtime service routines are responsible for 
> preserving the application?s tagmask whenever the runtime must perform DMA 
> synchronization. The application?s tagmask is preserved either by fetching 
> the current tagmask or by shadowing the application tagmask setting.
> 
> The remaining thirty tag ID?s (0 through 29) are available for application 
> use."
> 
> We abandoned tag ID partitioning because it wasn't required.  Before 
> making this code change, we need to fully understand why this partitioning 
> is needed, and if appropriate, open an RFC to standardize it.

The tag 16-31 are rejected by the kernel even without this change. I
don't know the reason why they are reserved for the kernel.

--
(ASAYAMA Kazunori
  (asayama at sm.sony.co.jp))
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